Activity 2.6 NCERT Class 10 Science, Acids, Bases and Salts

Activity 2.6 NCERT Class 10 Science, Chapter 2 Acids, Bases, and Salts.


This activity asks us to add a few drops of phenolphthalein into dilute sodium hydroxide and see what happens when we add dilute acid.

Observation: Adding phenolpthalein into dilute sodium hydroxide turns the solution pink. Now, when we add dilute acid in it, a time comes when solution become colurless again.


Phenolphthalein in basic solution,.

Phenolphthalein is a colourless reagent. It gives the pink to the solution at basic PH while at acidic PH the solution remain colour less. So, It is used in an acid-base titration to see the endpoint. In the above experiment ist solution is basic so we see pink colour. Subsequent addition of dilue acid neturalises the solution and at the end makes the solution acidic. As a result, the pink colour disappears.

Note:If we add dilute base after adding acid then situation will reverse and the solution gets own previous pink colour.

Basic solution + phenolpthalein  ⇒ Pink colour

Acidic solution + phenolpthalein  ⇒ Colourless

Inference/conclusion: A change in colour of PH indicator can indicate the completion of a reaction.

Next: Metal oxides react with acids to form its salt, Activity 2.7.

Read also: Metal carbonate reacts with acids to form carbon dioxide, Activity 2.5.

See the discussion on some other PH Indicators at Activity1.1.


Know more about phenolphthalein, Wikipedia.

10 thoughts on “Activity 2.6 NCERT Class 10 Science, Acids, Bases and Salts”

  1. Very useful , before reading this it was hard to understand. But now after going through these pages ,it made me understood these activities very clear to me.
    Thank you studdy.

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